package cn.element.leetcode.stage1;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * 给定一个包含n 个整数的数组nums和一个目标值target，判断nums中是否存在四个元素 a，b，c和 d，使得a + b + c + d的值与target相等？
 * 找出所有满足条件且不重复的四元组。
 *
 * 注意：答案中不可以包含重复的四元组。
 *
 * 示例 1：
 *
 * 输入：nums = [1,0,-1,0,-2,2], target = 0
 * 输出：[[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
 *
 * 示例 2：
 *
 * 输入：nums = [], target = 0
 * 输出：[]
 */
public class L18FourSum {

    public List<List<Integer>> fourSum(int[] nums, int target) {

        List<List<Integer>> lists = new ArrayList<>();

        if(nums == null || nums.length < 4){
            return lists;
        }

        Arrays.sort(nums);  //先排序一手

        int length = nums.length;

        for (int i = 0; i < length - 3; i++) {
            if(i > 0 && nums[i] == nums[i-1]){
                continue;
            }

            if(nums[i] + nums[i+1] + nums[i+2] + nums[i+3] > target){
                break;
            }

            if(nums[i] + nums[length-3] + nums[length-2] + nums[length-1] < target){
                continue;
            }

            for (int j = i + 1; j < length - 2; j++) {
                if(j > i + 1 && nums[j] == nums[j-1]){
                    continue;
                }

                if(nums[i] + nums[j] + nums[j+1] + nums[j+2] > target){
                    break;
                }

                if(nums[i] + nums[j] + nums[length-2] + nums[length-1] < target){
                    continue;
                }

                int left = j + 1,right = length - 1;

                while(left < right){
                    int sum = nums[i] + nums[j] + nums[left] + nums[right];

                    if(sum == target){
                        lists.add(Arrays.asList(nums[i],nums[j],nums[left],nums[right]));

                        while(left < right && nums[left] == nums[left+1]){
                            left++;
                        }

                        left++;

                        while(left < right && nums[right] == nums[right-1]){
                            right--;
                        }

                        right--;
                    }else if(sum < target){
                        left++;
                    }else{
                        right--;
                    }
                }
            }
        }

        return lists;
    }

    public static void main(String[] args) {

        L18FourSum a = new L18FourSum();

        int[] arr = new int[]{1,0,-1,0,-2,2};

        System.out.println(a.fourSum(arr,0));

    }
}
